PURPOSE: To provide a pulsation adjusting mechanism for a nonpulsating pump capable of limiting pulsation irrespective of pump actuating conditions.

CONSTITUTION: An increasing cam curve for increasing a part of the discharging flow rate of a main pump P is set on an eccentric cam and a reducing auxiliary pump (p) for adjustably reducing a part of the discharging flow rate of the main pump P is set on a driving shaft 14. The cam curve is set correcting the eccentric cam. The auxiliary pump (p) is composed of an auxiliary eccentric cam 44 including a cam 40 provided with a groove on the driving shaft 14 and engaging balls 42 and a spring back type plunger pump for reciprocating an auxiliary cross head 48 via a spring 46 (also an auxiliary plunger 54 linked there with via working oil 52 within a tube 50). A screw means 56 is provided capably of advancing and retreating on the engaging balls 42 so as to adjust the stroke length of the cross head 48 (thus the plunger 54) by engaging therewith.